A summary of the method used to produce these projections is provided below. For more detailed information on the method, and how assumptions made about future fertility, mortality and overseas and internal migration were formulated, see Chapter 2—Assumptions of Population Projections, Australia 2004 to 2101 (cat. no. 3222.0).

METHOD

The Australian Bureau of Statistics (ABS) uses the cohort-component method for producing population projections. In this method, assumptions made about future levels of fertility, mortality, overseas migration and internal migration are applied to a base population (split by sex and single year of age) to obtain a projected population for the following year. The assumptions are then applied to this new (projected) population to obtain a projected population for the next year. This process is repeated until the end of the projection period is reached.

These projections span the period June 2004 to June 2101 for Australia, and June 2004 to June 2051 for the states, territories, capital cities and balances of state.

The base population for all geographic areas is the revised estimated resident population (ERP) at 30 June 2004.

WHICH PROJECTION SERIES TO USE

Future uncertainty, along with the subjective nature of assessing current trends, means that using a range of possible outcomes rather than a single projection series gives a more realistic view of the possible future size, distribution and age structure of Australia's population.

The ABS has produced 72 alternative projection series using different combinations of assumptions on fertility, mortality, overseas migration and interstate migration. Different series are appropriate for specific time horizons (shorter or longer term), the region being studied and any volatility in the components. All series can more or less accommodate possible future levels of fertility and mortality as both are fairly predictable. However, there is less certainty of future levels of overseas migration and interstate migration given their historical volatility. This volatility will occur over time due to future government policies and decision-making and economic, social and other determinants and influences.

Detailed information for the three main series (Series A, B and C in the table below) are provided in the following data cubes:

Population Projections for Australia, 2004–2101—in SuperTABLE format,

Population Projections by Capital City/Balance of State, 2004–2051—in SuperTABLE format, and

Projected Population, Components of Change and Summary Statistics, for Australia, States and Territories, Capital City/Balance of State—in Microsoft Excel format.

The projections are also available in Time Series Spreadsheet (Microsoft Excel) format.

Detailed information for the remaining series can be made available on request by contacting the National Information and Referral Services on 1300 135 070 or Matthew Montgomery on 02 6252 6487. A charge is usually incurred for provided this data service. The ABS is also able to produce customised projections to meet specific requirements.

SUMMARY OF ASSUMPTIONS

Assumptions have been formulated on the basis of demographic trends over the past decade and longer, both in Australia and overseas, in conjunction with consultation with various individuals and government departments at the national and state/territory level. They do not attempt to allow for non-demographic factors (such as major government policy decisions, economic factors, catastrophes, wars) which may affect future demographic behaviour.

As future levels of fertility, mortality, overseas migration and internal migration are unpredictable, two or more assumptions have been made for each component. These are intended to illustrate a range of possible future outcomes, although there can be no certainty that any particular outcome will be realised, or that future outcomes will necessarily fall within these ranges.

FERTILITY

For the fertility component, assumptions are made about future total fertility rates (TFRs), age-specific fertility rates, and the sex ratio at birth. Three assumptions have been made about Australia's future TFR:

high assumption: the TFR will increase to 1.9 babies per woman by 2018, and remain constant thereafter;

medium assumption: the TFR will decline to 1.7 babies per woman by 2018, and remain constant thereafter; and

low assumption: the TFR will decline to 1.5 babies per woman by 2018, and remain constant thereafter.

Under all three scenarios the trend towards older ages of mothers at birth of children is assumed to continue to 2018, and then remain constant. The sex ratio at birth is assumed to be 105.5 male births per 100 female births for all years.

MORTALITY

For the mortality component, assumptions are made about future levels of life expectancy at birth for males and females. Two assumptions have been made:

medium assumption: life expectancy at birth will reach 84.9 years for males and 88.0 years for females by 2050–51, and remain constant thereafter. Under this assumption life expectancy at birth will increase by 0.40 years per year for males and 0.30 years per year for females until 2005–06, then by 0.30 years per year for males and 0.25 years per year for females until 2010–11, after which mortality improvement will gradually decline until 2050–51; and

high assumption: life expectancy at birth will reach 92.7 years for males and 95.1 years for females by 2050–51 and remain constant thereafter. Under this assumption male and female life expectancy at birth will increase by 0.40 years per year for males and 0.30 years per year for females until 2005–06, then by 0.30 years per year for males and 0.25 years per year for females until 2050–51.

For both assumptions, the change in age/sex-specific death rates derived from 1991–2002 mortality data is assumed to continue until 2025–26. Thereafter, the age-specific death rates are scaled to conform to the assumed life expectancy at birth for future years.

OVERSEAS MIGRATION

Three assumptions have been made about Australia's future levels of net overseas migration (NOM):

high assumption: annual NOM gain will increase to 140,000 people per year by 2007–08 and remain constant thereafter;

medium assumption: annual NOM gain will be constant at 110,000 people per year throughout the projection period; and

low assumption: annual NOM gain will decline to 80,000 people per year by 2007–08 and remain constant thereafter.

A zero net overseas migration assumption has been included to facilitate analysis of the impact of overseas migration to Australia's future population.

INTERSTATE MIGRATION

Three assumptions have been made about future net interstate migration levels:

high assumption: 'large' net population gains and losses for the states and territories;

medium assumption: 'medium' net population gains and losses for the states and territories; and

low assumption: 'small' net population gains and losses for the states and territories.

The medium series assumptions are based on long-term averages for the states and territories, while the high and low series provide for a range of possible future outcomes.

PROJECTION SERIES, Assumptions used

HIGH LIFE EXPECTANCY AT BIRTH

MEDIUM LIFE EXPECTANCY AT BIRTH

Net
interstate migration
(high)(a)

Net
interstate
migration
(medium)

Net
interstate migration
(low)(a)

Net
interstate migration
(high)(a)

Net
interstate
migration
(medium)

Net
interstate migration
(low)(a)

HIGH FERTILITY (TFR = 1.9)

Net overseas migration (per year)

140,000

1(A)

2

3

4

5

6

110,000

19

20

21

22

23

24

80,000

37

38

39

40

41

42

0

55

56

57

58

59

60

MEDIUM FERTILITY (TFR = 1.7)

Net overseas migration (per year)

140,000

7

8

9

10

11

12

110,000

25

26

27

28

29(B)

30

80,000

43

44

45

46

47

48

0

61

62

63

64

65

66

LOW FERTILITY (TFR = 1.5)

Net overseas migration (per year)

140,000

13

14

15

16

17

18

110,000

31

32

33

34

35

36

80,000

49

50

51

52

53

54(C)

0

67

68

69

70

71

72

(a) High and low interstate migration refer to high/low flow scenarios, and will therefore reflect high/low losses rather than high/low gains in some jurisdictions.

NATURE OF PROJECTIONS

The nature of the projection method and inherent fluctuations in population dynamics mean that care should be taken when using and interpreting the projection results. The projections are not exact forecasts but simply illustrate future changes which would occur if the stated assumptions were to apply over the projection period. The projections do not attempt to allow for non-demographic factors (eg. major government policy decisions, economic factors, catastrophes, wars) which may affect future demographic behaviour.

LIABILITY

It is important to recognise that the projection results given in this report simply reflect the assumptions made about future fertility, mortality and migration trends. While the assumptions are formulated on the basis of an objective assessment of past demographic trends and their likely future dynamics, there can be no certainty that they will be realised.

No liability will be accepted by the Australian Bureau of Statistics for any damages arising from decisions or actions based upon these population projections.

For further information on population projections refer to the ABS publication Population Projections, Australia 2004 to 2101 (cat. no. 3222.0). For further information, including quotes on the preparation of alternative projections, please contact:

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